INSULIN AND C-PEPTIDE SECRETION IN NON-INSULIN-DEPENDENT DIABETES-MELLITUS AND ITS RESPONSE TO DIETARY THERAPY

We studied insulin and C-peptide levels in patients with non-insulin-d ependent diabetes mellitus (NIDDM) during standard oral or intravenous glucose tolerance tests (GTT) at the time of diagnosis and after 3 mo nths dietary therapy. On the second occasion they also had an 'augment ed' GTT, in which slow intravenous infusion of glucose raised basal pl asma glucose to a level similar to that at the time of diagnosis. Eigh t patients had oral tests, and seven patients intravenous tests. In bo th groups, dietary therapy significantly reduced fasting and peak plas ma glucose (p<0.05 for oral; p<0.01 for intravenous GTT). Serum insuli n levels during conventional oral GTT were not significantly different after dietary therapy compared to diagnosis, but were significantly h igher during the 'augmented' oral GTT (p<0.05). In those patients who underwent intravenous GTT, there was a significant increase in both th e total amount of insulin secreted (0-60min) and in first-phase insuli n secretion (0-10 min) during the 'augmented' test compared to diagnos is (p<0.01), but first-phase insulin secretion during the conventional intravenous GTT was unchanged. Serum C-peptide responses were also gr eater during 'augmented' tests (p<0.05), similar in pattern to serum i nsulin. There is a relative deficiency in insulin secretion in untreat ed NIDDM, which can be reversed by dietary therapy. It is essential to study insulin and C-peptide secretion in controlled 'fasting' glucose conditions.